1. Field of the Invention
The present invention relates to a feeder of oxygen gas containing steam of high purity and distributed uniformly for use in heat treatment process of semiconductor manufacturing in which a heated wafer of semiconductor is fed with oxygen gas containing steam, and the steam is deposited on the surface of the semiconductor wafer to form an oxide film thereon serving as a protective coat.
2. Description of Prior Art
Hitherto, as one of feeders of oxygen gas containing steam of this kind, a feed for bubbling method is well known as shown in FIG. 7. According to this prior feeder, oxygen gas is blown into pure water 2 stored in a sealed vessel 1 in the direction of arrow as shown in FIG. 7, and the oxygen gas damped by passing through the pure water 2 is fed. By such method, however, since a vessel or reservoir is used for pure water storage, it is impossible to maintain the purity required in manufacturing a semiconductor device. Moreover, there is a drawback in its operability since the pure water has to be often changed or replenished in the vessel.
In order to meet such drawbacks, a so-called pyrogenic method is popularly used these days as shown in FIG. 8. According to this recent method, oxygen gas is induced to a quartz tube 4 in which semiconductor wafers 8 are aligned on a supporting board 9 by way of an induction pipe 5, while hydrogen gas is induced to such oxygen gas atmosphere by way of an induction pipe 6, and steam is generated by combustion of the induced hydrogen gas. Then oxygen gas containing the generated steam is deposited on the surface of the semiconductor wafers 8 to form an oxide film thereon. In FIG. 8, numeral 7 denotes a flame of hydrogen and 10 denotes a heater disposed along the outer wall of the quartz tube 4.
3. Problems to be Solved
By the aforementioned pyrogenic method, indeed it is possible to maintain a purity required in the semiconductor manufacturing porcess, but there still exist following drawbacks:
(1) It is hard to control the hydrogen flame, and there is the possibility of failure in ignition, which may cause explosion.
(2) Front end of the hydrogen flame may sometimes reaches the surface of the semiconductor wafer and damages it.
(3) Uneven gas stream in which only down stream portion of the hydrogen flame contains high steam may be generated, whereby the result of solid surface treatment becomes ununiform particularly in the case of a semiconductor wafer of large diameter, eventually causing a problem of quality of such wafer.
In order to meet such drawbacks, several attempts have been proposed. According to one of them, the quartz tube is elongated so as to have a larger distance between the hydrogen flame and the semiconductor wafer. According to Japanese Patent Publication (examined) No. Sho 59-53697, a nozzle of special design is proposed for induction of hydrogen gas. Further, as a method for achieving uniformity of hydrogen gas content, a separate combution chamber system is employed wherein a combustion chamber is separated from a heat treatment chamber of semiconductor wafer, and both chambers are communicated with each other through a connector.
Even when employing such separate system, the problem of above (1) still remains unsolved, and moreover inner wall surface of the combustion chamber is damaged by the hydrogen flame resulting in a further problem of mixing impurities in the gas.